FIG. 1E is a driving circuit of a conventional piezoelectric activation element, which is disclosed in Japan Patent No. JP2004282988A. The driving circuit shown in FIG. 1E could only charge and discharge the single-side electrode of the piezoelectric activation element 11, so the vibration amplitude of the piezoelectric activation element 11 could only reach a half level. FIG. 1F is a driving circuit of another conventional piezoelectric activation element, which is disclosed in US Patent No. US20070046143A1. In FIGS. 1E and 1F, the source of driving signal is generated by the electrodes of the piezoelectric elements 11, 13, which is to make the piezoelectric material being vibrated with its own natural oscillation frequency. However, this kind of driving method would make the driving frequency for the piezoelectric material generated by the circuit could not be arbitrarily changed.
FIG. 1G is a clock frequency generation chip 15 used in a driving circuit of a conventional piezoelectric activation element. The clock frequency generation chip 15 is used as a generation unit for driving period. When the clock frequency generation chip 15 outputs a driving signal with a certain frequency, it has to externally connected with other passive elements, such as resistors and capacitors, except for increasing the circuit layout space, when the resistors or capacitors have the variation of resistance or capacitance due to external conditions, such as temperature, it would seriously affect the precision for the driving signal of the output frequency. Moreover, when the circuit layout is completed, if it is required to change the output frequency of the driving signal, it has to adjust or replace together with the periphery passive elements, so that the flexibility for variation of circuit would be greatly limited, and the piezoelectric activation element could not be applied with intermittent driving function.
FIG. 1A to 1D are various waveform diagrams for the alternate driving voltages V2 driving the piezoelectric activation elements in the prior art, which sequentially are the sine waveform, triangular waveform, square waveform, and quasi-square waveform. In FIG. 1A, we first define the half-wave leading edge 10 as the waveform for charging on the piezoelectric activation element, and the half-wave trailing edge 12 as the waveform for discharging on the piezoelectric activation element, and the half-wave leading edge 10 and the half-wave trailing edge 12 both form a “half wave.”
Both the sine wave in FIG. 1A and the triangular wave in FIG. 1B are belonging to the analogy driving waveform. Comparing with the driving wave of square wave in FIG. 1C and quasi-square wave in FIG. 1D, the circuit designs for FIG. 1A and FIG. 1B are more complicated, and required for more layout components, so the required layout space is also larger, which is the defect of the circuit design.
The square wave in FIG. 1C and the quasi-square wave in FIG. 1D are belonging to the digital driving waveform, in which the designed circuits have the advantages of simple layout and rapid discharging. As seen on the half-wave leading edge in FIG. 1C and FIG. 1D, the circuit would proceed rapid charging on the piezoelectric activation element, although the rapid charging would make the piezoelectric driving element fast reaching the peak of the amplitude, and also increase the power consumption. Moreover, because of the rapid charging on the piezoelectric element, after the piezoelectric activation element reached the peak of the amplitude and before the activation of the piezoelectric activation element in opposite direction, the piezoelectric driving element would vibrate in natural oscillation frequency until the piezoelectric activation element is discharged and activated toward the opposite direction. Thus, the natural vibration would also cause the problem of larger noise.
Furthermore, as seen in FIG. 1D, the waveform of the alternate driving voltage is provided with the features of fast charging and slow discharging, except for the more power consumption. The half-wave trailing edge in FIG. 1D is gradually descending in a slope, which indicates that the piezoelectric activation element could not have rapid discharging, so as to delay the time required for entering the next charging and discharging period, and further affect the activation reaction time for the piezoelectric activation element.